Non-woven spun-bond webs formed from filaments or fibers are typically made from a thermoplastic resin on an apparatus such as that disclosed in U.S. Pat. No. 5,814,349, the disclosure of which is incorporated herein by reference. Such apparatus typically includes a spinneret for producing a curtain of strands and a process-air blower for blowing process air onto the curtain of strands for cooling same to form thermoplastic filaments. The thermoplastic filaments are then typically, aerodynamically entrained by the process air for aerodynamic stretching of the thermoplastic filaments which are then, after passing through a diffuser, deposited upon a continuously circulating sieve belt or fabric for collecting the interentangled filaments and forming a web thereon. The web, so formed, is then subject to further processing. An exemplary apparatus of this type, particularly for high-speed spun-bond web production, is currently available from Reifenhauser GmbH Co. Maschinenfabrik, Troisdorf, Germany and sold under the name Reicofil®. Other exemplary forming machines are available from Oerlikon Neumag, Neumunster, Germany.
Such equipment endeavors to operate at higher and higher speeds. Most of the high-speed technology involves less than 2 denier filament base webs, with the highest speed spinning relative to less than 1 denier, termed micro denier webs. The high-speed spinning involves high velocity, small diameter fibers that will naturally exhibit bounce at impact, due to the high-speed, and bleed through the sieve belt or fabric, due to their small size relative to fabric open area. Also, in some machines fabrics need to allow for the removal of excessive quantities of air in “sealed” type arrangements as disclosed in the aforesaid patent. In other machines, there is no sealed chamber, but the material drains onto a web. In such a situation, accordingly it is desirable to have a fabric with high permeability, low bleed, and sufficient topography to avoid uncontrollable fiber “splashing” during deposition. Also, new high-speed systems place the diffuser close to the fabric which increases both the magnitude and quantity of high velocity vertical impingement of fiber onto the fabric.
Current fabrics or belts used in high-speed spun-bond manufacturing lines are a compromise between good hold down and excessive bleed through. For example, while a fabric may provide for good hold down of the web, it may do so at the expense of fiber penetration and bleed through into the fabric or belt. Alternatively, while a fabric may limit bleed through of deposited filaments, it does so at the expense of web hold down. One exemplary fabric is discussed in U.S. Pat. No. 7,578,317, the disclosure of which is hereby incorporated herein in its entirety. Another exemplary fabric is discussed in International Patent Publication WO 09/030033, the disclosure of which is hereby incorporated herein by reference. It may be desirable to provide other fabrics for spun-bond manufacturing lines, particularly those that operate at high speeds.